Certain patients present in a paroxystic manner symptoms of a bradycardia condition, such as unexplained syncopes, but without a presenting bradycardia condition that can be observed and documented by a conventional temporary external recording of the Holter type.
To make it possible for a practitioner to pose a diagnosis and to decide whether a pacemaker implant is an appropriate therapy, it has been proposed to implant a device with purely diagnostic objectives, making it possible to record information of the heartbeat rate in order to confirm whether various symptoms observed in the patient have a “rhythmic cause,” that is, a heartbeat rhythm (or lack of rhythm) that leads to the observed symptoms that is detected and to be treated. One such device is the Reveal® Insertable Loop Recorder, available from Medtronic, Inc. However this device does not comprise any means for providing cardiac stimulation and is designed not to have an endocardial probe so as to simplify its implantation. Therefore, this device does not offer any help in the event of an occurrence of a severe bradycardia whose consequence can be extremely noxious for patients having a risk of ventricular arrhythmia.
It would be certainly possible to implant in the patient, on a purely prophylactic basis, a complete pacemaker equipped with suitable Holter memory functions. Such an apparatus, initially, could then be used only for its Holter capabilities, in order to record information on the heartbeat rate at the time the symptoms are evoked by the patient, in order to confirm or not whether the symptoms have a rhythmic cause. But to be able to record the spontaneous cardiac activity of the patient, it is of course necessary to inhibit the cardiac stimulation function of the pacemaker device. In this example, it is not convenient to activate the stimulation means, because the indication for a therapeutic stimulation by the apparatus has not yet been demonstrated; however, according to the patient, the presence of a pacemaker and the acceptance of a surgical operation for its implantation make intolerable the persistence of symptoms that are sometimes severe, and whose consequences can be extremely serious. It would be thus essential in this example to envisage providing a back-up ventricular stimulation.
However, a traditional pacemaker would not be adapted to this situation. Indeed, the base stimulation frequency cannot be programmed with a sufficiently low value to let the spontaneous ventricular rhythm be expressed at the time of a bradycardia. And, even if the pacemaker could have a rather low base frequency value, that value would be fixed and arbitrary, and could thus appear insufficient or unsuited for the patient. It is indeed not possible to define a priori the ventricular back-up stimulation frequency, which must be sufficiently low so as not to disturb the recording of the spontaneous cardiac activity, and sufficiently high not to let too severe a bradycardia be expressed.
The compromise sought is thus impossible to find in a general manner, because the threshold of the severity of a bradycardia giving rise to symptoms is specific to each patient.